JPH01254797A - Production of mesophase pitch - Google Patents

Abstract

PURPOSE:To obtain a homogeneous mesophase pitch having a low softening point and suitable for producing high-strength carbon fibers, by subjecting mesophase pitch prepared in a separation step to steps for removing quinoline- insoluble and n-heptane-soluble portions. CONSTITUTION:Mesophase pitch obtained in a step for separating mesophase pitch is subjected to the first solvent extraction treatment with a solvent using an aromatic hydrocarbon based solvent, quinoline and pyridine as an extracting reagent so as to provide about 0.01-20wt.% concentration of quinoline-insoluble portions in the pitch. The resultant pitch is then subjected to the second solvent extraction treatment for removing n-heptane and treated so as to provide about 0.01-5wt.% concentration of n-heptane-soluble portions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing mesoface pitch suitable for producing carbon fibers and shaped carbon materials. More specifically, the present invention relates to a method for producing mesoface pitch, which is suitable as a raw material for high-strength, high-modulus, high-performance carbon fibers and molded carbon materials.

[Prior art]

BACKGROUND ART Conventionally, there has been a demand for the development of high-performance materials having light weight, high strength, high elastic modulus, etc. in various industrial fields such as automobiles, aircraft, etc., and carbon fiber has been attracting attention from these viewpoints.

Currently, commercially available carbon fibers are still PAN-based carbon fibers made from polyacrylonitrile, but carbon fibers made from coal or petroleum pitches are also cheaper raw materials, have a higher yield in the carbonization process, and have more elasticity. It is regarded as important due to its advantages such as the ability to obtain fibers with high fiber content, and active research and development efforts are being carried out.

Carbon fiber obtained from optically isotropic pitch has a strength of 1
Although both the modulus of elasticity is low, high-performance carbon fibers can be obtained from optically anisotropic pitch (i.e., mesoface pitch) obtained by heat-treating optically isotropic pitch. These methods include, for example, simply heat-treating the raw material pitch (Japanese Patent Laid-Open No.
9-19127 and 57-42924), extracting the optically isotropic pitch with a solvent and heat-treating the insoluble matter (Japanese Patent Application Laid-open No. 160427/1984, etc.), and blowing inert gas. (Japanese Patent Application Laid-Open No. 58-1686
No. 87), heat treatment after partial hydrogenation (Japanese Unexamined Patent Publications Nos. 57-100186 and 58-18421)
, terminating the pyrolysis polycondensation in the middle and performing sedimentation separation or centrifugation depending on the difference in specific gravity to obtain highly concentrated anisotropic pitch (Japanese Patent Publications No. 61-38755 and No. 62-24036)
Several methods have been proposed.

However, depending on the use of these mesoface pitches, PA
Although fibers with ultra-high elastic modulus and high elastic modulus can be easily obtained for all N-based carbon fibers, they are still insufficient to develop high strength.

As a result of intensive studies on the production of mesoface pitch for obtaining high-strength carbon fibers, the present inventors determined that the mesoface pitch obtained in the mesoface separation process was treated with a first solvent for removing quinoline insoluble components. The present invention was completed based on the discovery that a mesoface pitch that can exhibit high strength during carbon fiber production can be obtained by subjecting it to an extraction treatment and a second solvent extraction treatment for removing n-heptane soluble components.

〔the purpose〕

The object of the present invention is to be able to develop high strength. The object of the present invention is to provide a method for stably producing mesoface pitch, which has a low softening point and is extremely homogeneous, and is suitable for producing pitch-based carbon fibers.

〔composition〕

According to the present invention, a heat treatment step of heat-treating a carbonaceous raw material to produce mesoface-containing pitch, and a mesoface pitch in which mesoface pitch is obtained by separating the produced mesoface-containing pitch into a mesoface pitch component and a non-mesoface pitch component. In a method for producing mesoface pitch including a separation step, the mesoface pitch obtained in the mesoface pitch separation step is subjected to a first solvent extraction treatment for removing quinoline insoluble components and a first solvent extraction treatment for removing n-heptane soluble components. A method for producing mesoface pitch is provided, which comprises subjecting the pitch to a second solvent extraction treatment.

That is, in the method for producing mesoface pitch of the present invention, the mesoface pitch obtained in the mesoface pitch separation step is subjected to a first solvent extraction treatment for removing quinoline insoluble components, thereby removing the quinoline insoluble components. It will be done. By removing components with significantly different molecular sizes and solid substances that would inhibit the development of high strength when made into carbon fibers, and further subjecting the fibers to a second solvent extraction treatment to remove n-heptane soluble components. 1, which shows high strength when made into carbon fiber by removing components that inhibit mesophasing.
A homogeneous mesophase pitch with a narrow molecular distribution is obtained.

In addition, the mesoface pitch (i.e., optically anisotropic pitch) referred to in the present invention refers to a pitch in which brightness is observed by polishing the cross section of a pitch lump solidified at room temperature and rotating crossed nicols with a reflective polarizing microscope. In other words, it means a pitch in which most of the pitches are substantially optically anisotropic, and pitches that are optically isotropic without any brilliance are referred to as non-mesoface pitches (optically isotropic) in this specification. It is called directional pitch).

Therefore, the mesophase pitch in the Suiza book includes not only a pure optically anisotropic pitch but also an optically isotropic phase contained in an optically anisotropic phase in the form of a spherical or irregularly shaped island. This also includes cases where On the contrary, non-mesophase pitches also include those containing a small amount of optically anisotropic phase in optically isotropic pitches. There are also two types of memface: those that are insoluble in quinoline or pyridine, and those that contain a large amount of components that are soluble in quinoline or pyridine.
The mesophase referred to herein is primarily the latter mesophase.

Furthermore, the mesophase content in the present invention is determined by observing and photographing a sample under crossed Nicols using a polarizing microscope and measuring the area ratio occupied by mesophase portions in the sample. The softening point of pitch in the present invention refers to the same-liquid transition temperature of pitch, which is determined from the peak temperature of absorption and release of latent heat during melting or solidification of pitch using a differential scanning calorimeter. be. This temperature agrees within a range of ±10°C with those measured by other ring-and-ball methods, *i melting point methods, etc. for pitch samples.

Hereinafter, the method for manufacturing mesoface pitch of the present invention will be explained in detail.

The present invention includes a heat treatment step of heat-treating a carbonaceous raw material to produce mesoface-containing pitch, and a mesoface pitch separation step of separating the generated mesoface-containing pitch into a mesoface pitch component and a non-mesoface pitch component to obtain mesoface pitch. It also includes a post-treatment step consisting of a first solvent extraction step for removing quinoline insoluble components and a second solvent extraction step for removing n-heptane soluble components.

Various so-called heavy hydrocarbon oils, tars, or pitches can be used as the carbonaceous raw material for producing mesoface pitch used in the present invention.

Examples of these raw materials include various heavy petroleum oils, asphalt (e.g. straight asphalt,
blown asphalt, etc.), pyrolysis tar, catalytic cracking tar, heavy oil, tar, pitch obtained by carbonization of coal, or heavy liquefied coal produced from one coal liquefaction process, etc. Suitable examples include catalytic cracking residual oil of petroleum. These are used after being subjected to preliminary treatments such as filtration and solvent extraction, if necessary. Furthermore, in order to stabilize the quality of the mesophase pitch produced by the present invention, carbonaceous pitch, which partially already contains a small amount of mesophase pitch as a result of the pyrolysis polycondensation reaction, may be used as a raw material.

The heat treatment step for producing mesophase-containing pitch is a step for performing a meso-formation reaction (defined as a reaction for producing mesophase) by pyrolysis polycondensation reaction. The thermal decomposition polycondensation reaction is a reaction in which the thermal decomposition reaction of one heavy hydrocarbon and the polycondensation reaction occur in parallel as main reactions.
Refers to a reaction that changes the chemical structure of pitch component molecules,
As a result of this reaction, scission of the paraffin #'1 structure, dehydrogenation, ring closure, development of a planar structure of polycyclic condensed aromatics due to polycondensation, etc. proceed.

For this reaction, the carbonaceous feedstock is heated to about 380°C to about 460°C.
, preferably heat treated at 400-430°C. If the reaction temperature exceeds about 460° C., the volatilization of unreacted raw materials increases, the softening point of mesophase increases, and coking is likely to occur, which is unsuitable.

On the other hand, if the temperature is lower than about 380°C, the reaction will take a long time, which is not preferable.

In the heat treatment process, stirring is performed to prevent local overheating and to ensure uniform reaction, but in addition, stirring is performed under reduced pressure or as necessary to quickly remove low molecular weight substances generated as a result of thermal decomposition. This can be carried out while blowing an inert gas into the reactor. In this case, the inert gas may be nitrogen, water vapor, carbon dioxide, light hydrocarbon gas, or a mixed gas thereof, which has sufficiently low chemical reactivity with pitch at one reaction temperature.

It is preferable to preheat these inert gases before blowing them in without lowering the reaction temperature.

The inert gas containing cracked oil gas is extracted from the upper part of one reactor and sent to a condenser and a scrubber.

The cracked oil and gas are removed through a separation tank and the like. the .

Afterwards, it is also possible to recycle and use the inert gas.

This heat treatment reactor is usually made of a cylindrical container, and is equipped with a raw material supply port, a discharge port for cracked oil, cracked gas, inert gas, etc., a pitch extraction port, a non-mesoface pitch introduction port (described later), etc. 1 A stirring device and the like are provided inside the reactor, and a heater and the like are provided outside.

In the heat treatment step of the present invention, the mesophase component is brought to a state in which the produced pitch is substantially free of low molecular weight decomposition products and unreacted substances and contains about 30 to about 80%, preferably about 380 to about 70%, of the mesophase component. When this happens, it is preferable to stop the process and transfer to the next mesoface pitch separation process. This is because in order to obtain a high yield of homogeneous mesophase pitch with a low softening point in the mesophase pitch separation process, it is necessary to have a high pitch yield after the pyrolysis polycondensation reaction and a mesophase content of approximately 20 to 20%. This is because it is preferable that the softening point is about 80% or less and the softening point is 260°C or less. If the mesophase component in the pitch after the pyrolysis polycondensation reaction is less than 20 meters, the yield of mesophase pitch in the next separation step will be extremely low, and conversely, if the mesophase component is increased to more than 80%, If the softening point is higher than 260° C., the separability in one separation step will deteriorate, making it impossible to obtain mesoface pitch with a high concentration, and the obtained mesoface pitch will have a high softening point. The mesoface-containing pitch obtained in this process has a diameter of 5.
Spherical particles with a weight of 00μ or less, preferably 300μ or less are suitable.

2. In the present invention, since a post-treatment step consisting of a first solvent extraction treatment for removing quinoline insoluble components and a second solvent extraction treatment for removing n-heptane soluble components is provided, the mesophase described below It is permissible to generate mesoface pitch in the heat treatment process, which has a high softening point or contains a small amount of low molecular weight substances, within a range that does not deteriorate the separability in the pitch separation process. There is no need to take any measures regarding conditions, and stable heat treatment can be performed.

In the present invention, the mesoface-containing pitch produced in the heat treatment step is sent to the next mesoface pitch separation step, where it is separated into mesoface pitch components and non-mesoface pitch components. Various known solid-liquid separation methods can be appropriately employed to separate mesoface pitch and non-mesoface pitch, but in particular, a separation method using a difference in specific gravity (see Japanese Patent Publication No. 38755/1983) , No. 62-24036) is preferred, and particularly in industrial production, centrifugation is preferred.

In the centrifugal separation method, mesophase-containing pitch generated in a heat treatment process is subjected to a centrifugal separation operation in its molten state, whereby the mesophase component quickly settles because it has a higher specific gravity than the isotropic component.

As it coalesces and grows, it accumulates in the lower layer (layer in the direction of centrifugal force), and approximately 80% or more of the mesophase forms a continuous phase, which contains a slight isotropic phase in the form of islands or minute spherules. The mesoface pitch is the lower layer.

-The upper right layer is mostly an isotropic phase, with a non-mesophase pitch in which mesophases are dispersed as minute spherical bodies, and the interface between the upper and lower layers is clear. This method utilizes the fact that the specific gravity of the upper layer and the lower layer in the molten state is significantly different, and the lower layer is separated and taken out from the upper layer to separate mesoface pitch and non-mesoface pitch. The centrifugal separation operation is a processing operation that applies high-speed rotation to a fluid, collects a phase with a higher specific gravity in the fluid to a lower layer (in the direction of J center force), and separates this, and is one of its embodiments. As such, operation using a so-called centrifugal separator, particularly a continuous type centrifugal separator that continuously separates and discharges a heavy phase and a light phase, is advantageously used.

The temperature in this step depends on the magnitude of centrifugal force, but is preferably above the softening point of the mesophase-containing pitch, preferably from 280°C to
The temperature is 400°C, more preferably 320°C to 380°C. A predetermined constant temperature within this range may be used, and the temperature does not necessarily have to be constant.

In this step, the main purpose is to deposit and coalesce many parts of the mesophase in the direction of centrifugal force, and it is necessary to avoid thermal decomposition and polycondensation reactions as much as possible. Therefore, a temperature higher than 400° C. is not preferable, and a temperature higher than necessary makes it difficult to operate the centrifugal separator continuously for a long time, but there is no such problem at the above-mentioned temperature. Furthermore, at temperatures lower than the above range, the viscosity of the pitch system as a whole, especially of the mesophase component, is high, making it difficult for the isotropic phase co-precipitated in the lower mesophase to come off, giving rise to a long and extremely large centrifugal acceleration. It also becomes difficult to separate.

The centrifugal force acceleration of the centrifugation operation may be of any value, but the mesophase component (heavy phase) and non-mesophase component (light phase) can be efficiently separated in a short time by shortening the residence time. Preferably 1,0OO
G or more, particularly in the range of 10,000 to 40,000 OOG can be adopted. Note that there are restrictions in terms of equipment when using 50,000 OOG or more.

From this process, the mesophase content is 90% or more, especially 95%.
% or more of mesoface pitch can be obtained economically in a short time.

In addition, the non-mesoface pitch separated in this step can be converted into pitch containing menphace by applying heat treatment again, so in a preferred embodiment, this non-mesoface pitch is subjected to the heat treatment step at a specific point in time. is circulated.

In order to avoid broadening the residence time distribution (i.e., molecular weight distribution) of mesophase in the heat treatment process, this cycle ensures that the physical properties of the pitch produced in the heat treatment process are the same as those of the non-mesophase pitch. It is preferable to do this at the same time.

This circulation of non-mesoface pitch causes it to undergo heat treatment again, improving the final pitch yield.

In addition, in the present invention, it is also possible to add an appropriate finishing heat treatment step immediately after the mesoface pitch separation step. That is, if a particularly short residence time is used in the separation step, the softening point is sufficiently low.

A slightly insufficient mesoface pitch with a mesoface content of approximately 80% to 90% is produced, and then this is heated at 300°C to
It is also possible to adopt a method of adding a thermograviding reaction treatment at a temperature of 430° C. to adjust the properties of the mesoface pitch to within narrow quality control limits.

Mesoface pitch containing 80 to 90% mesophase contains 10 to 20% isotropic components, but this isotropic component can be further reduced by adding a small amount of thermal weighting reaction treatment, and it can also be softened. It is known that the mesophase content gradually increases, so by thermograviding the pitch after one minute using appropriately controlled temperatures and treatment times, the mesophase content can be increased to 90% or more, preferably 95% or more. can be adjusted to

In the present invention, the mesoface pitch separated in the mesoface pitch separation step (or the mesoface pitch that has undergone the final heat treatment in the case where the final heat treatment has been applied) is then subjected to a first process to remove quinoline insoluble components. Sent to solvent extraction process.

That is, the mesoface pitch is usually 21 to 80% by weight.
However, after undergoing the first solvent extraction treatment, the concentration of the quinoline insoluble component is usually 0.01 to 20.
% by weight, preferably about 0.1 to 5% by weight,
At the same time, its softening point also decreases.

Examples of the oil agent used in the first solvent extraction step include aromatic hydrocarbon solvents such as benzene, toluene, and xylene, as well as quinoline and pyridine, which may be used alone or in combination. You can also do it. This process usually uses an oil to mesoface pitch ratio of 50:1 to 3:1,
It is carried out at a temperature of 70 to 330'C and a pressure of from atmospheric pressure to 50 Kg/aJ, and the quinoline-insoluble components are separated from the mesoface pitch as an extraction residue. In addition, when carrying out this step, it is also possible to adopt a method in which the extraction agent is kept under supercritical conditions and brought into contact with mesoface pitch. It is preferable because it has effects such as improving the transferability of quinoline-soluble components) to the extract.

The solid substance mainly composed of quinoline insoluble components is separated from the mesoface pitch-oil mixture by means such as filtration and centrifugation, and is further separated from the liquid consisting of the mesoface pitch-oil mixture by vacuum stripping, vacuum evaporation, etc. The extractant is removed by the means. The extractant can be recovered and reused.

In the present invention, the mesoface pitch that has undergone the first solvent extraction treatment is further sent to a second solvent extraction treatment step for removing n-heptane soluble components.

That is, mesoface pitch that has undergone the first solvent extraction treatment usually contains 5 to 30% by weight of n-heptane soluble components, but the concentration of n-heptane soluble components usually decreases by the second solvent extraction treatment. 0.01-5 weight 2, preferably 0.1
~3 weight, and at the same time its softening point increases.

Examples of the oil used in this second solvent extraction process include saturated hydrocarbon solvents having 3 to 10 carbon atoms, such as propane, butane, pentane, hexane, heptane, octane, nonane, and decane. They may be used or may be used in combination. Also boiling point 250℃
The following petroleum hydrocarbons such as gasoline fractions, naphtha, and kerosene fractions can be used in winter. This process typically uses an oil to mesoface pitch ratio of 10:1-1:1. Temperature 25~
The process is carried out at 300° C. and a pressure ranging from atmospheric pressure to 30 g/ci, and n-heptane soluble components are separated from the mesoface pitch as extracted components.

The n-heptane soluble component-extractant mixture is separated from the mesoface pitch by means such as filtration, centrifugation, etc. Any remaining oil in the pitch is removed by conventional vacuum stripping, vacuum evaporation, or other means. Of course, after stripping the extractant from the filtrate consisting of the n-heptane soluble component-extractant mixture, it is preferable to reuse the separated oil agent.

The pitch obtained in this process is continuously taken out of the system and remains in a liquid state or is solidified to become a product.

From this process, the softening point is sufficiently low, that is, 230℃~3
A pitch in the range of 20°C, preferably 250°C to 300°C is obtained.

The pitch obtained as described above is melt-spun according to a known method, and the obtained pitch fibers are made infusible, carbonized, and optionally further graphitized to produce high-performance pitch-based carbon fibers. Graphite fibers can be obtained.

〔effect〕

According to the present invention, the mesoface pitch separated in the mesoface pitch separation step is further subjected to a first solvent extraction treatment for removing quinoline insoluble components and a second solvent extraction treatment for removing n-heptane soluble components. By adding carbon fibers, it is possible to stably obtain a pitch that can exhibit high strength when made into carbon fibers, has a low softening point, and has good spinnability during spinning. Furthermore, by proceeding to graphitization, pitch-based graphite fibers with high strength and ultra-high modulus of elasticity can be produced.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is of course not limited thereto.

Example Tar produced as a by-product during catalytic cracking of petroleum is converted to normal pressure at 4
Distilled under reduced pressure to 50℃, and further distilled the obtained tar to 100℃
The tar obtained by centrifuging at 10,0 OOG and then using an electrostatic precipitator to remove solids from the tar was used as a starting material.

13 kg of the raw material tar after the solid content was removed was put into a heat treatment reactor with a stirrer with a content of +120Q, and while blowing nitrogen gas from the top of the reactor, it was heat treated at 415°C for 5.5 hours to produce mesophase-containing pitch. I got it.

The mesoface content of this mesoface-containing pitch is 5
5%, and the pinch yield was 33% by weight.

After the heat treatment reaction in the reactor, the mesophase-containing pitch was extracted from the bottom of the reactor, introduced into a continuous centrifugal separator for mesophase separation, and continuously heated at 350°C for 10 minutes.
Centrifugation was performed at a centrifugal force of .0OOG to separate mesophase components and non-mesophase components. The mesoface content in the mesoface pitch component was 97%, and the softening point of the pitch was 325°C. Further, the concentration of quinoline insoluble components in the pitch was 60% by weight, and the concentration of n-heptane soluble components was 6.3% by weight.

The mixture was mixed at a ratio of 1 part of mesoface pitch to 10.0 parts of quinoline, and held at 200° C. for 30 minutes under atmospheric pressure to perform a first solvent extraction treatment. After the first solvent extraction treatment, 1
Centrifugation was performed at 0.0OOG to separate the extract and extraction residue. From the extract, quinoline, which is an extraction solvent, was removed by vacuum distillation to obtain pitch. The softening point of the pitch is 261°C.

The concentration of quinoline insoluble components was 1.2% by weight, and the concentration of rhohebutane soluble components was 15% by weight. Moreover, the yield of the pitch was 38.5% by weight based on the pitch after centrifugation.

This pitch was mixed at a ratio of 3.0 parts n-heptane to 1 part pitch, and was held at 98°C for 30 minutes to perform a second solvent extraction process. After the second solvent extraction process, 10,0OOG
Centrifugation was performed to separate the extract and pitch. The n-heptane remaining in the pitch was removed by vacuum evaporation. The softening point of this pitch was 280°C, the concentration of quinoline insoluble components was 1.3% by weight, and the concentration of rhohebutane soluble components was 0.8% by weight2. The yield of this pitch was 23% by weight based on the pitch after centrifugation.

This pitch was put into a spinning machine having a nozzle with a diameter of 0.3 nvwφ, melted at 330° C., extruded with a nitrogen gas pressure of 200+m+Hg, and wound for 30 minutes at a speed of 500 m/min. The spinnability during this spinning was extremely good, and there was no yarn breakage.

11) A part of the pitch fiber was held at 230°C for 2 hours in an oxygen atmosphere of J'g to make it infusible, and then heated to 1,500°C at a rate of 30°C/min in nitrogen gas. The tensile strength of the obtained carbon fiber was 3.9 GPa, and the tensile modulus was 280 GPa.
Comparative Example 1 The first mesoface pitch after centrifugation in Example
When spinning was carried out in the same manner as in the example without performing the solvent extraction treatment and the second solvent extraction treatment, the spinnability was poor, with a score of 10.
The yarn broke three times during the minute of spinning.

This pitch fiber was heated to 1,500°C in the same manner as in the example.
The carbon fiber obtained by raising the temperature to 2.4 GPa has a tensile strength of
The tensile modulus was 250PGa.

Comparative Example 2 The mesoface pitch after centrifugation in Example was treated in the same manner as in Example, except that the second solvent extraction treatment was not performed.

In this case, the spinnability during spinning was good, but some of the fibers were fused during infusibility. Also, when made into carbon fiber, the tensile strength is 3.5 GPa, and the tensile modulus is 27.
0 GPa, and showed lower physical properties compared to the examples.

Patent applicant: Toa Fuel Industries Co., Ltd.

Claims (4)

[Claims] (1) A heat treatment step in which a carbonaceous raw material is heat-treated to produce mesoface-containing pitch, and a mesoface pitch separation step in which the generated mesoface-containing pitch is separated into a mesoface pitch component and a non-mesoface pitch component to obtain mesoface pitch. In the method for producing mesoface pitch, the mesoface pitch obtained in the mesoface pitch separation step is subjected to a first solvent extraction treatment for removing quinoline insoluble components and a second solvent extraction treatment for removing n-heptane soluble components. A method for producing mesoface pitch, the method comprising subjecting it to an extraction process. (2) The method according to claim 1, wherein the first solvent extraction process uses at least one of an aromatic hydrocarbon solvent, quinoline, and pyridine as an extractant. (3) The method according to claim 1 or 2, wherein the concentration of quinoline insoluble components in the pitch after the first solvent extraction treatment is 0.01 to 20% by weight. (4) The method according to any one of claims 1 to 3, wherein the concentration of n-heptane soluble components in the pitch after the second solvent extraction treatment is 0.01 to 5% by weight. .